FIGS. 7(a)-7(d) are sectional views illustrating a method of fabricating a semiconductor laser device according to the prior art. Initially, in the step of FIG. 7(a), after an n type Al.sub.0.4 Ga.sub.0.6 As lower cladding layer 2, an Al.sub.0.1 Ga.sub.0.9 As active layer 3, and a p type Al.sub.0.4 Ga.sub.0.6 As upper cladding layer 4, and a p type GaAs cap layer 5 are successively epitaxially grown on the front surface of an n type GaAs substrate 1, an SiO.sub.2 film is formed on the p type GaAs cap layer 5 and then etched away so that the SiO.sub.2 film is left only on a striped region of the cap layer 5. Next, using the remaining SiO.sub.2 film 70 as a mask, the p type GaAs cap layer 5 and a part of the p type AlGaAs upper cladding layer 4 is etched away, and a portion to be an optical waveguide under the SiO.sub.2 film 70 (hereinafter, referred to as optical waveguide region) is left as shown in FIG. 7(b). In the step of FIG. 7(c), n type GaAs current blocking layers 6 are selectively grown so as to bury the etched portion. Next, in the step of FIG. 7(d), after the removal of the SiO.sub.2 film 70, a p type GaAs contact layer 7 is grown on the entire surface of the cap layer 5 and the current blocking layers 6. Further, an n side electrode (a rear surface electrode) 101 is formed on the rear surface of the n type GaAs substrate 1 and a p side electrode (a front surface electrode) 102 is formed on the surface of the p type GaAs contact layer 7, respectively. When a forward bias voltage is applied between the n side and the p side electrodes of the semiconductor laser device fabricated as described above, and a current flowing in the semiconductor laser device is larger than a threshold current of the laser, laser oscillation occurs. At this time, the current flowing into the semiconductor laser device is concentrated in the optical waveguide region by the current blocking layers. Therefore, electrons and holes are effectively injected into the active layer of the optical waveguide region, and then laser oscillation occurs in the active layer of the optical waveguide region due to the recombination of electrons and holes. Also in S. Yamashita et al., "High-Power 780 nm AlGaAs Quantum-Well Lasers and Their Reliable Operation," IEEE Journal of Quantum Electronics, vol.27, pp.1544-1549, June 1991, the fabricating method of the semiconductor laser device as described above is disclosed.
In the prior art method of fabricating the semiconductor laser device, since the selective growth mask for the current blocking layer 6 comprises the SiO.sub.2 film containing a large quantity of oxygen, the GaAs of the current blocking layer 6 is partly adhered on the SiO.sub.2 film during the selective growth of the current blocking layer 6. In the etching generally used for removing the SiO.sub.2 film, GaAs is not etched. For example, though SiO.sub.2 is dissolved in a hydrofluoric acid based etchant used for etching SiO.sub.2, GaAs is not dissolved in this etchant. Therefore, when the SiO.sub.2 film is etched, the SiO.sub.2 film directly under the GaAs which is adhered on the SiO.sub.2 film is not etched and is left on the surface of the p type GaAs cap layer 5, and so this causes an imperfect growth of the contact layer 7 formed on the cap layer 5. When the imperfect growth of the contact layer 7 occurs, the electrical resistance of the contact layer 7 is increased and light output is lowered.
In addition, in the process for selectively growing the current blocking layer and the process for cooling the layer after the growth, dislocations are produced in the semiconductor layer by a shearing stress between the SiO.sub.2 film 70 and the p type GaAs cap layer 5 and penetrates the active layer 3 of the optical waveguide region. Further, by operating this laser device, dislocations propagate in the active layer 3, and the recombination of electrons and holes is non-radiative in the vicinity of the dislocations. Such a non-radiative region in the vicinity of a dislocation is called a dark line. Due to the generation of dark lines, the light output power of the laser device is reduced.